1. Field of the Invention
The present invention generally relates to computer-aided circuit design systems, and more particularly to a system and method for evaluating a netlist of a very large scale integrated (VLSI) circuit for various potential design errors.
2. Discussion of the Related Art
Integrated circuits are electrical circuits comprised of transistors, resistors, capacitors, and other components on a single semiconductor xe2x80x9cchipxe2x80x9d in which the components are interconnected to perform a given function such as a microprocessor, programmable logic device (PLD), electrically erasable programmable memory (EEPROM), random access memory (RAM), operational amplifier, or voltage regulator. A circuit designer typically designs the integrated circuit by creating a circuit schematic indicating the electrical components and their interconnections. Often, designs are simulated by computer to verify functionality and ensure performance goals are satisfied.
In the world of electrical device engineering, the design and analysis work involved in producing electronic devices is often performed using electronic computer aided design (E-CAD) tools. As will be appreciated, electronic devices include electrical analog, digital, mixed hardware, optical, electromechanical, and a variety of other electrical devices. The design and the subsequent simulation of any circuit board, VLSI chip, or other electrical device via E-CAD tools allows a product to be thoroughly tested and often eliminates the need for building a prototype. Thus, today""s sophisticated E-CAD tools may enable the circuit manufacturer to go directly to the manufacturing stage without costly, time consuming prototyping.
In order to perform the simulation and analysis of a hardware device, E-CAD tools must deal with an electronic representation of the hardware device. A xe2x80x9cnetlistxe2x80x9d is one common representation of a hardware device. As will be appreciated by those skilled in the art of hardware device design, a xe2x80x9cnetlistxe2x80x9d is a detailed circuit specification used by logic synthesizers, circuit simulators and other circuit design optimization tools. A netlist typically comprises a list of circuit components and the interconnections between those components.
The two forms of a netlist are the flat netlist and the hierarchical netlist. Often a netlist will contain a number of circuit xe2x80x9cmodulesxe2x80x9d which are used repetitively throughout the larger circuit. A flat netlist will typically include multiple copies of the circuit modules essentially containing no boundary differentiation between the circuit modules and other components in the device. By way of analogy, one graphical representation of a flat netlist is simply the complete schematic of the circuit device.
In contrast, a hierarchical netlist will only maintain one copy of a circuit module which may be used in multiple locations. By way of analogy, one graphical representation of a hierarchical netlist would show the basic and/or non-repetitive devices in schematic form and the more complex and/or repetitive circuit modules would be represented by xe2x80x9cblack boxes.xe2x80x9d As will be appreciated by those skilled in the art, a black box is a system or component whose inputs, outputs, and general function are known, but whose contents are not shown. These xe2x80x9cblack boxxe2x80x9d representations, hereinafter called xe2x80x9cmodulesxe2x80x9d, will mask the complexities therein, typically showing only input/output ports.
An integrated circuit design can be represented at different levels of abstraction, such as the Register-Transfer level (RTL) and the logic level, using a hardware description language (HDL). VHDL and Verilog are examples of HDL languages. At any abstraction level, an integrated circuit design is specified using behavioral or structural descriptions or a mix of both. At the logical level, the behavioral description is specified using Boolean equations. The structural description is represented as a netlist of cells, sometimes referred to herein as leaf cells. Examples of leaf cells include full-adders, NAND gates, latches, and D-Flip Flops.
Having set forth some very basic information regarding the representation of integrated circuits and other circuit schematics through netlists, systems are presently known that use the information provided in netlists to evaluate circuit timing and other related parameters. More specifically, systems are known that perform a timing analysis of circuits using netlist files. Although the operational specifics may vary from system to system, generally such systems operate by identifying certain critical timing paths, then evaluating the circuit to determine whether timing violations may occur through the critical paths. As is known, timing specifications may be provided to such systems by way of a configuration file.
One such system known in the prior art is marketed under the name PathMill, by EPIC Design Technology, Inc. (purchased by Synopsys). PathMill is a transistor-based analysis tool used to find critical paths and verify timing in semiconductor designs. Using static and mixed-level timing analysis, PathMill processes transistors, gates, and timing models. It also calculates timing delays, performs path searches, and checks timing requirements. As is known, PathMill can analyze combinational designs containing gates, and sequential designs containing gates, latches, flip-flops, and clocks. Combinational designs are generally measured through the longest and shortest paths.
While tools such as these are useful for the design verification process after layout, there are various shortcomings in the PathMill product and other similar products. For example, there is often a need to identify certain circuit configurations that may lead to operational uncertainty or performance problems. However, VLSI circuits contain numerous circuit primitives. Indeed, VLIS circuit often contain thousands of gates. As a result, design tools that are configured to evaluate VLSI circuits often identify numerous errors. Therefore, error listings, or listings that identify potential errors, may be very lengthy and therefore difficult, if not overwhelming, for a designer to deal with.
Accordingly, there is a heretofore unaddressed need to provide a design tool that evaluates a netlist or other electronic file representative of a VLSI circuit design to identify potential errors and generate lists of such potential errors, in a manner that is very manageable for the designer.
Certain objects, advantages and novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the advantages and novel features, the present invention is generally directed to a system and method for evaluating a very large scale integrated circuit design in a structured, hierarchical fashion. In accordance with one aspect of the invention, a method evaluates a first circuit portion for a variety of potential errors and generates a first list of potential errors identified in the first circuit portion. The method further includes the step of adding at least one of the potential errors to a waiver file. The method further includes the step of examining a second circuit portion for a variety of potential errors, except those errors listed in the waiver file.
In one embodiment, the step of examining the second circuit portion may be executed in a variety of ways. In one embodiment, the step may be configured to evaluate the second circuit portion for a number of potential errors. For any error(s) so identified, the method may add the errors to an error listing that is to be reported. However, the method may then exclude or omit from this listing any errors (or tests) listed in a waiver file. Alternatively, the method may be configured to evaluate a second circuit portion for a number of predefined potential errors. However, before evaluating the second circuit portion for the various potential errors, the method may first examine the waiver file and exclude errors listed therein from the second examination step. That is, rather than examining the second circuit portion for all potential errors, the method may examine the second circuit portion for all potential errors (predefined), except those listed in a waiver file.
In accordance with one embodiment of the present invention, the method may also consult and/or utilize the waiver file in connection with the examination of the first circuit portion, in the same way that it consults/utilizes the waiver file in connection with the examination of the second circuit portion. In accordance with yet a further embodiment of the invention, the first circuit portion may correspond to one or more leaf cells, while the second circuit portion may include a larger circuit that encompasses the one or more leaf cells.